This invention relates to the production of alkali metal silicate. In particular, the invention is an improved method for preparing highly alkaline silicate such as sodium metasilicate wherein the unreacted raw materials are confined to the central portion of the furnace by bubbles eminating from bubblers placed around the periphery of the furnace.
Soluble silicates that have mole ratios of about 1 M.sub.2 O:1 SiO.sub.2 can be prepared by subjecting the proper mixture of sand and alkali metal source, generally the carbonate, to temperatures of 2000.degree. F. or higher, thereby producing the molten silicate. The major problems encountered in the production of materials such as sodium metasilicate relate to the corrosive nature of the alkali metal source and its tendency to attack the refractories used to construct the furnace. These attacks not only damages furnace structures, but are also responsible for the major portion of the impurities found in the product.
One solution to the problems encountered in preparing highly alkaline silicate is found in U.S. Pat. No. 2,950,570 to Cowels and Shaver. This patent teaches a method of forming alkaline silicate upon a bed of previously formed, solid alkali silicates in a furnace with walls constructed of water cooled metal chambers. The raw materials are charged to such a furnace and melted using burners. The material forms a quiescent pool of molten alkaline silicate. This molten material solidifies against the water cooled metal chambers so that the corrosive molten alkali metal source does not contact the walls. This system requires large volumes of cooling water, but is also unsuitable as it requires excessive amounts of energy. The cooled surfaces act as heat sinks so that substantial amounts of heat are removed from the system and cannot be utilized in the fusion process. The operation is also energy intensive because the reacting materials must be maintained in the quiescent pool for an extended period of time to achieve homogeneous character. Motion in this pool is restricted to thermally induced currents which are sluggish and therefore, inefficient in mixing the batch. In addition, the hardware required to implement this system is complicated and expensive. The metal chambers forming the furnace walls must have the capacity to respond to changes in the volume of molten material in the furnace. The transverse position of the metal cooling chambers is adjustable which is a further complication of this hardware.
It is an object of this invention to prepare highly alkaline soluble silicates that do not contain impurities from contact of the molten alkali source with the refractory walls. It is also an object to provide alkaline silicate with low impurity levels without the need for cooling water or adjustable metal chambers. It is a further object of this invention to produce homogeneous products in a short fusion time in an agitated pool of molten material.